Stable newborn infants in the Maimonides NICU who are being nursed under a radiant warmer will be studied. As part of routine care, the thermistor probe will be applied and the desired servocontrolled skin temperature set. Once stabilized, a trimmed reflective shield to cover only the probe itself will be placed over the thermistor probe. Changes in measured skin temperature and warmer power output will be recorded non-invasively, as well as the time taken to reestablish baseline status. A full-sized reflective shield will then be placed over the thermistor probe and the same observations recorded, then repeated 15 minutes later. At the time of a subsequent routine change in thermistor position, the same procedure will be followed, but omitting the intermediate step of using the smaller trimmed shield. Continuous core temperatures will be monitored via a short rectal probe during the study periods.